1. Field of the Invention
The present invention relates to a machining method, a program, a machining-program generating program and a machining apparatus of a press die.
2. Description of Related Art
As shown in FIG. 11, a press die for, for instance, punching a vehicle door includes a pierce cutter B formed along an outer circumference of a die body and a secondary relief-clearance area C recessed inward relative to the profile of the pierce cutter B, the pierce cutter B and the secondary relief-clearance area C being arranged in a piercing direction. The secondary relief-clearance area C is provided so that punched piece punched by the pierce cutter B is not hooked on the press die.
Traditionally, in order to machine such a press die, the entire process is divided into two steps, i.e. machining of the pierce cutter B and machining of the secondary relief-clearance area C.
When the pierce cutter B is to be machined, as shown in FIG. 12, a flat-end mill is used as a machining tool, which is moved along a profile line of the pierce cutter B to carve the outer circumference of a press die material W, leaving a finishing margin (approximately 0.5 to 1.0 mm) from the profile line of the pierce cutter B (coarse machining).
During the machining of the secondary relief-clearance area C, as shown in FIG. 13, a T-shaped tool (T-shaped tool provided with a short cylindrical blade on an end of a tool shaft) is used as a machining tool, which is moved along the profile line and is moved up and down by an operator while defining the pierce cutter B to machine the secondary relief-clearance area C.
Incidentally, as an alternative method for machining the secondary relief-clearance area without using the T-shaped tool shown in FIG. 13, it is proposed to use a carving tool having a tapered end-mill portion, a ball-end mill or a carving tool having a spherical end-mill portion at an end thereof to machine the secondary relief-clearance area of a press die (See Document 1: JP-A-2006-192485).
After completion of the above machining, i.e. after completion of the coarse machining of the pierce cutter B and the machining of the secondary relief-clearance area C, finish machining is conducted on the pierce cutter B.
During the finish machining, as shown in FIG. 14, the coarsely machined pierce cutter B is carved with a flat-end mill for about 0.5 to 1.0 mm to finish the pierce cutter B. Subsequently, as shown in FIG. 15, the pierce cutter B is tapered (relief cutting) except for an effective blade B1 at an end (approximately 2 mm) to provide a blade relief-clearance area B2.
In the traditional machining methods, it is proposed to machine the secondary relief-clearance area with various tools, all employing two stages, i.e. machining of the pierce cutter and machining of the secondary relief-clearance area. Since different types of tools are used in the respective steps, labor and cost are required for exchanging the tools, resulting in poor efficiency.
Especially, since the machining of the secondary relief-clearance area requires that an operator manually moves the T-shaped tool up and down while defining the pierce cutter to machine the secondary relief-clearance area while leaving the portion corresponding to the pierce cutter, skilled work is necessary and some degree of danger is accompanied.
It is conceivable that the pierce cutter and the secondary relief-clearance area are machined successively conducted with a single tool of elaborated configuration, which, however, requires larger tool length. Then, on account of resistance received by the tool during carving, the tool is bowed away from the workpiece. Accordingly, considering the flexure of the tool, multiple separate carving processes with slight carving amount are required, so that significant reduction of machining time cannot be expected.